An optimized assay for prekallikrein activator activity in human plasma products

Prekallikrein activator (PKA) assay is described. PKA was measured indirectly by allowing it to generate kallikrein from prekallikrein and then measuring the amidolytic activity of kallikrein by using the synthetic chromogenic substrate S-2302. It was ensured that sufficient amounts of substrates were included in both enzymatic phases of the assay, and the pH and ionic strength which seemed to be very important in the assay were carefully controlled. Both a kinetic assay and a simple endpoint assay are described. Other amidolytic enzymes probably present in plasma products are also estimated and a correction is made to exclude their role in the assay result. The precision of the kinetic assay is characterized by the coefficient of variation of 3.1% within an assay and the reproducibility by that of 4.8% between assays. For the endpoint assay both values are 4.8%.